High-Speed FBG Interrogation for Multi-Point Lithium-Ion Battery Temperature Monitoring Using a REC-DFB Laser Array

Lithium-ion batteries can undergo rapid and spatially nonuniform temperature variations during high-rate operation, requiring multi-point temperature monitoring with high temporal resolution for effective thermal management. This work presents a high-speed fiber Bragg grating (FBG) temperature monitoring system based on a reconstruction-equivalent-chirp distributed feedback (REC-DFB) laser array. The developed 24-channel REC-DFB laser array, integrated with an on-chip optical combiner and semiconductor optical amplifier, achieves a continuous wavelength-sweeping range of approximately 50 nm, with a tuning range of approximately 2.4 nm per channel and channel power equalization. To suppress temperature-strain cross-sensitivity caused by battery deformation, strain-isolated FBG temperature sensors with polyimide packaging are developed, exhibiting sensitivities of 9.7-10.4 pm/°C over 20-80 °C with coefficients of determination (R²) above 0.998. Battery experiments are performed at discharge rates up to 4 C, with simultaneous FBG and thermocouple measurements at the top, middle, and bottom positions. The proposed system achieves an interrogation rate of 5 kHz and shows good agreement with thermocouples under slowly varying thermal conditions. During rapid thermal transients at 4 C, the peak temperature rises measured by the FBGs are 2.1-2.6 °C higher than those measured by the thermocouples, while a maximum temperature-rise difference of 5.98 °C is observed across the battery surface. These results demonstrate the capability of the proposed all-solid-state, mechanically scan-free system for high-speed, multi-point monitoring of dynamic and spatially nonuniform thermal behavior in lithium-ion batteries.